fix: address CodeRabbit review comments for encryption key persistence

- Always mirror encryption key to both .env and WRITEPATH (Docker safety)
- Guard array key access with isset() before reading in Encryption.php
- Fix encrypt_value() to not treat string '0' as empty
- Improve error logging for failed encryption attempts

app/Config/Encryption.php

@@ -147,6 +147,7 @@ class Encryption extends BaseConfig
         $data = json_decode($content, true);
         if (
             !is_array($data)
+            || !isset($data['key'])
             || !is_string($data['key'])
             || strlen($data['key']) < 64
         ) {